The present invention pertains to axial piston pumps of the type substantially comprising a plurality of pistons inserted into a fixed cylinder block and in contact with an inclined plate carried by the rotary shaft of the pump, an annular valve member, a pressure limitating device and a distribution chamber having two parallel faces with symmetrically disposed ports. These material elements are so conditioned that the position of the valve member may be modified with respect to that of said inclined plate, during the functioning of the pump, by means of a helical groove device. Such type of pump is well known and is for instance described in the US Pat. No. 3.074.345.
Such known pumps, although acceptable for low outputs, show serious limitations as to size and cannot work at high pressures, due to their very own characteristics.
It has indeed been established that the axial reaction on the inclined plate and transmitted to the shaft of the pump increases as the square of the dimensions of the pump whereas the longevity of the mechanical abutments and bearings decreases hyperbolically in function of the square of the load.
Above 30 to 33 cc/round and for actually accepted pressures from 300 to 400 bars, for instance, the longevity of the pump becomes inferior to the requirements of the actual market.
It has already been proposed to hydrostatically compensate the above-mentioned axial reactions by means of a by-pass circuitry establishing a communication between the two faces of aforesaid inclined plate. Such a solution, described for instance in the French Pat. No. 1.409.274, is not satisfactory in that it gives rise to pressure losses and to reso-nances, due to the unavoidable length of said by-pass ducts.